Current state-of-the-art immunosuppressive strategies have been most successful at inhibiting acute rejection and have significantly improved short-term graft survival rates. However, these same strategies have failed to interrupt the development of, and more importantly, the progression of chronic allograft rejection. Since chronic allograft rejection is currently the leading cause of graft failure following solid organ transplantation, it has become most apparent that there is a great need to develop new paradigms and models in order that novel therapeutics can be developed to target this process. The prevailing view is that the nature or magnitude of the immune response to donor antigen determines the rejection process. In addition, it is thought that the phenotype of the immune response (and the local inflammatory cytokine milieu) determines the activation state of the allograft. However, it is evident from recent studies that the graft itself, and not the immune response, can be dominant to shape the rejection process (even in the face of immune tolerance). Consistently, several studies have identified the activation state of the graft endothelial cell (EC) as a determinant of acute and chronic rejection. Furthermore, recent studies indicating that mTOR inhibitors target graft EC indicate that the effect of these agents to attenuate the progression of chronic rejection (and chronic vascular disease(s)), may be associated with their ability to target the EC activation response. Nevertheless, to date, the select role of the graft EC in the development of rejection has been difficult to study. In EC, mTOR signals enhance the activity of the kinase Akt, which in turn regulate many EC activation responses. In this exploratory research proposal, we plan to utilize the unique VE-Cadherin:tTA+/TET-Akt+ double transgenic mouse, in which it is possible to regulate Akt selectively within the endothelium. We will use hearts from this mouse as donors of cardiac transplants such that we can: Aim 1, develop a transplantation model to study the select role of Akt-inducible and EC activation responses in the chronic rejection process;Aim 2, evaluate the dominance of the graft EC in the development of chronic rejection, and Aim 3, study the effect of Akt-induced activation of donor EC in immune regulation and tolerance. The development of this unique model of chronic rejection will provide us with an exciting opportunity for the first time to directly assess the role and functional effect of the graft EC in the development of chronic allograft rejection and/or in the maintenance of alloimmune tolerance. PUBLIC HEALTH RELEVANCE: Organ transplantation is a life saving therapy for individuals with end stage organ failure. However, despite the development of novel immunosuppressive strategies, all transplants eventually fail due to a reaction called chronic allograft rejection. While currently dogma dictates that the immune response is the major determinant of acute rejection, additional events within the graft also dictate the development and progression of chronic rejection. In this research proposal we will develop a novel and unique transgenic mouse model in which we will establish whether the graft itself, and specifically the vasculature within the graft is a major functional determinant of this process. Our goal is to develop new paradigms to understand and treat chronic rejection.